Heat, rust, and acid resisting ferrous alloy



March 22, 1932. P. A. E. ARMSTRONG HEAT, RUST, ANDy ACID RESISTING FERROUS ALLOY Filed June 19, 1925 Vis'iemea11010.22, 1932 'Y 1,350,953 f u UNITED STATES PATENToFFicE PiinoY A. nnitias'riioire, or' New Yoan, ir. Y. naar, ausm, Aim nein ansisrme Emmons ALLOY Application filed J'une- 19, 1925..Y Serial N'o. 38,170.

My invention relates to a ferrous alloy conalloys that have to withstand 1700 degrees F., taining chromium, aluminum and iron with and line 3 the minimum alloy content that or Without oarbon.- Manganesecan be used, Vshould be used if a temperature of 1550 dealso high melting point elements, and silicon grees F, is to be employed. The representacan be used to replace in part the necessary tion of the chart does not afford an absolute- 55 aluminum content in about the same volume ly accuraterepiesentaton for obviously no as the portion of aluminum replaced. hard and tast line can be drawn'as the con- My alloy will contain the usual phosphorus k ditions under which the allo Works', type ofA and sulphur generally found in high grade heat', and composition ot eated gases to i@ alloy irons. The phosphorus and sulphur which it is subjected all play an important o0 content should be kept low. part. Nevertheless the vchart affords a very The essential elements are aluminum, excellent guide for ordinary heat applicachromium, and iron. Aluminum can be retions and for short time runs at heat. The placed in part with silicon. The chromium following tabulation gives the analysis of a.

l@ content should be over'1% and under 20%, number of embodiments of my invention and 05 aluminum under 6%, silicon under 4%, manthe temperature at which they can generally ganese under 2%, carbon under 1.25% and run Without progressive scaling at elevated preferably under 75%. Nickel under 5% temperatures.

may be used, but the alloy ispreferably A Y nickel free, as nickel detracts from the heat Ttega 20 's' rti whichrh@ eshlhmg Surtcace PIOPQ es o or Ai si Mn Fe mmap- -iigh melting point elements such as tungpms to f Sten, molybdenum, uranium, zirconium, tan- Slrafun' talum, columbium, boron, vanadium, copper .and cobalt, should be under 5%` each, parig Egrem--- 155031?. :Z5 .5 ance-.. 1550 F. ticularly boron, which induces `great brittle .65 1 60 3.50 41 31 Balan ,5500K ness, unless the quantity used is very small. g8 y,gaanca r l1 Boron seems to have the eidectot maintain- 7,69 L25 20 .io Bn-. 1550r. L 9.1. .95 .54 '.46 Ba ance-.- 15.50 F.

, mg @L Smau Crystal. slze m he forgad bar .05 12.10 .20 .32 .sa Balamand. 1550F.

and in a small casting, about .001 to .002% ggm 80 or" boron-seems to be sucient. Io i'gg 9133 14s lgs gaanl i050; r1

.0 o. .25 2 aance.. 1700 F. Chromium ailid iroln alloyedt tsogl'thlei be` gg gs .l5 gaam, 17002K 0 0 '.60 sance--. 1700 F. come mcreasmh y'sca e T2515, an o lg? em .15 5.10 3.00 .20 .3i mimica-- 1700i. 6 peratures as the chromium content is in- 1 .g .2111 pliance--- 1100g ance..` 1700 u creased. is 9.05 3.00 .40 .42 Balance--- 1i0or. 85

This valuable property is greatly enhanced l, glggguggg in the lower ranges of chromium by addipaenne.-- tions of aluminum. 3% of chromium in iron :B gg :gg 21g lg gilf: 1700: FI .0 .1 6 ance.-- 1700 F. d@ with nearly 6% or' aluminum is as non cor 72 an '82 .31 45 Belangen 1,00., F ge rosive to heat oxidation at high temperatures, .Q9 1g .gg plianc--- L. all@ as 18 to 20% of chromium with practically 04 2.05 5 60 ,62 25 :saiau 1900 F, no aluminum ai .a a it ance... 1 0 n the accompanying drawing the single ggg ggg gggguggg figure is achart depicting in graphic form 150 slss 5.00 160 fig Balance: 19002 FI' S5 thescale breakdown 901m- Of mi' alloy at :S iti-82 tt :i3 :l tl: 1%; i: various temperatures. Line 1 represents in gg g-flg -gg llggggm a rough Way the minimum chromium andv loa plea 131 1180 1120 pugnali: 1900: p1 aluminum that can be used if the alloy is to jl ,j 114g gjj; ggg; i `G2 .6 0 aance-.- 0 5 withstand a temperature of 1900 degrees F. 1 25 i 5D 40 25 30 www" 1,50., E ,im

` line 2 the minimum alloy content for those lit All the foregoing examples can be forged.

Zr Va Nl Mo Or Al Si Mn Fe All the foregoing examples can be forged.

It will be observed on comparison with the chart that in the fifth sampleof the second list containing 3% of nickel, the scaling point 1s reduced by at least 150 F. by the nickel present.

The acid and rust resisting properties of the alloy are dependent upon the content of aluminum and chromium plus the amountof other elements also included. Generally speaking it is the iron that rusts, therefore, the less the quantity of iron present by volume the less the alloy will corrode in the atmosphere.

My alloy owes its non-corrosive property to its film forming characteristic and the great speed in which another film is formed in-the event of the protecting lm being broken. l

It is well known that aluminum has this property, hence it is generally considered to be non-corrosive to some atmospheres. This property is present in my alloy, though somewhat different in extent and kind.

The film that forms on my alloy is genl erally cathodic to the underlying metal and would cause corrosion in the presence of an electrolyte such as a damp atmosphere if -it were not for the non-porousnature of the film. Should the conditions to which the alloy is subjected be excessively corrosive, then the film becomes thicker and the alloy has the appearance of surface discoloration or even superficial rust. For resistance to hot oxida tion the film is generally sufiiciently protective if the alloy content of aluminum and ,chromium is at least 8% by volume of the total and more than 40% by volume is not necessary for the purposes of this invention. For atmospheric corrosion resistance I prefer to use not less than 12% by volume of the total alloying content. The alloy is increasingly resistant to all forms of corrosion as the alloying content is increased. Owing to the chromium content of my alloy itis not very resistant to sulphuric, hydrochloric or hydrofluoric acids, but they high volume content remesa alloys are very resistant to air diluted fumes or very dilute acids. Passivity is generally readily produced under these conditions.

Pickling the surface with nitric acid causes the alloy to take on an oxide like film that is very resistant to atmospheric corrosion. j Where circumstance'will permit I prefer a nitric acid pickle surface finish. The sur- I face of my alloy can be polished but care jshould betaken' not to scorch the surface, as by dry polishing, since such surface seems to I be very easily corroded.

Electrolytic pickling gives good results against atmospheric corrosion. I prefer t0 have the alloy the positive terminal of an j outside E. M. F., direct current, and if the pickling medium is chromic acid there is a very excellent oxide appearing film formed upon the surface of one alloy, which in this instance'is very heat resisting, beside being resistant to atmospheric corrosion.

The outside E. M. F. can be direct current of any ordinary voltage; 6 to 300 volts seems to work very well.

My alloy will not harden when quenched from high temperatures unless the carbon is carried tothe higher side of my limit. Where hardening is required the carbon should be over .20% and the aluminum under 5% if the chromium is on the low end of my range, and under 2% aluminum if the chromium is at the high end of my range.

Where hardening can be produced the alloy should be heatedto 1800 to 1950 F. and quenched in oil. Annealing for all analysis is preferably at 1550 to 1650 F. and slow cooling is necessary only if maximum softness is required.

If high carbon is employed the carbides will cause corrosion, as they are cathodic and the film that forms seems to be easily broken down by thesecathodic areas, therefore, the carbides should be rendered as harmless to the surface as possible by dissolving them as far as convenient by a heat treatment process. The carbides seem to fairly readily dissolve in the alloy if heated to about 1900 F. and can be maintained in the dissolved state by fairly speedy cooling as by quenching in oil. Subsequent reheating to remove strains and undesirable hardness, if any is present, will cause the surface to more readily discolor than if the alloy was not reheated after the carbide dissolving treatment. No advantage With respect to corrosion is obtained by heat treatment when the alloy is heat treated and afterwards subjected to hot oxidation. There are, of course, some physical advantages. Carbon seriously detracts from the scale resistant properties of the alloy. Therefore, unless high physical properties are required carbon should be as low as practical.

The high melting point elements,fsuch as tungsten, molybdenum, tantalum, columbium, vanadium, and zirconium have a marked effect upon the alloy as far as the physical properties are concerned, tending to raise the proportional limit in the soft condition and also to increase the strength of the alloy where raised to high temperatures, There does not seem to be any particular reason for using more than 5% each and generally 1% to 3% is sufficient. High melting point elements such as tungsten, tantalum, columbium and zirconium increase the resistance of the alloy to hot oxidation at temperatures, also add to the corrosion resistant surface film at atmospheric temperatures, and the resistance to corrosion arising from steam, salt water and the like. added properties are not present if the aluminum or aluminum and silicon content is very low, tha-tis under .25%.

Nickel somewhat improves the acid corrosion resistant property of my alloy and often adds to the toughness, it detracts from the scale resisting property of the alloy at high temperature, and adds to rolling and machine troubles, therefore, for general applications l leave it out.

ln melting my alloy I prefer to use an elecprefer tofkeep the nickel low or tric furnace, either induction type or the indirect arc, although the direct arc type can be used. Also Crucible melting can e employed.

The high aluminum content is not readily obtained as aluminum will readily reduce the slag and contained oxides, therefore, special attention has to be paid to the addition of this element, and the bath must be well degasified either by addition of aluminum to the molten metal or by some other degasifier.

The bath should be kept as cool as possible, preferably just above freezing point, before adding the aluminum. lf the slag is rich in Aalumina the aluminum loss is lower. Shutting od the arcs and letting the slag cool is very excellent way of preventing aluminum loss. The induction furnace is well suited to making the alloy because the slag is always Vfairly cool, as the current does not iiow through the slag as readily as through the metal. The basic furnace is well suited, as with an acid slag the silica is apt to be reduced, raising the silicon content to undesirable quantities. A very excellent way for making the addition of aluminum is to melt down in one furnace, add all the desired elements, except aluminum, then either just before pouring add molten or solid aluminum to the bath, or. teem the melt into a ladle and add the molten or solid aluminum at that time.

My alloy rolls very well and casts very solid. With about the middle range of aluminum it gives no trouble at all in rolling and pierces readily into tubes. If the aluminum high Thesel is carried to the upper limit more care has to y Y be exercised duringhot working.

The alloy to be pierced contains preferably not higher than 18% of chromium as a certain amount of brittleness is present with the high chromium content.

My alloy cold 'rolls very well and a high finish is readily produced for cold rolling or working. The carbon is preferably kept on the low side.

My alloy offers great resistance to abrasive Wear, which adapts it for many working arts thatrotate or reciprocate.-

y allow is particularly well suited for automobile engine valves because the protecting surface film is tightly adhering and of smooth surface texture, does not readily pick up bits or pit, the protecting film arising from the high aluminum alloyed with the chromium and iron is not of a Stic? nature that is present with chromium an 'silicon that is aluminum free.

With the carbon substantially over .20% the tappet ends ofthe valves, which are preferably made all in one piece, that is to say, formed from a single piece of metal, can be hardened so as not to be battered up by the cam or tappet blows, the stems run well in the guides and appear to take on wear resisting characteristics from rubbing in the guides, andthe valve head and valve seat do not scale when subjected to the very high heats encountered haust valves, for example.

My alloy gives excellent service used as containers subject to elevated temperatures, or for apparatus required to resist acids and liquid or atmospheric corrosion, such as saline solutions, sea water, river water, or various chloride solutions. For these purposes and where great malleability is desired, as particularly for cooking utensils, l prefer to use an alloy that has an alloying content of more than 12% by volume of the total, and having a ratio by volume of aluminum content to the chromium content of about l to 5. The lower the volumetric ratio, i. e. 2: 5, and so forth, of aluminum to chromium, with a given amount of chromium, the greater iii general is the resistance to corrosion by any medium to which the alloy is at all resistant.

The chart of the accompanying drawing can be used as a guide to choose alloys that are resistant to corrosion other than that due to hot oxidation. Generally speaking, the higher the temperature the alloy will withstand before beginning to scale progressively, the greater will be the resistance of a similar analysis in withstanding ordinary corrosion.

As shown in the examples set forth above, l have in two cases incorporated as many as three of the high melting point element-s and in other cases two of these elements, and as stated these may, if desired, be used in quantities up to 5% each. Also, as stated above,

in use, as in aeroplane exy the manganese content may range up to 2% and the carbon content may go as high as 1.25%, and these taken with two of the high melting point elements in their maximum quantity, together with the phosphorus and sulphur, make a total of approximately 14%. Thus when in the ensuing claims I use the phrase the balance being principally iron I intend that the sum of the iron, chromium, aluminum and silicon shall be not less than about 86%. of the whole.

I'claim:

1. A stable surface alloy steel which is resistant to hot oxidation and is readily workable containing about 9% chromium, about 3% aluminum, and silicon within the usual ranges encountered in steel makingl practice but not more than about 1%, the remainder being principally iron.

2. A stable surface alloy steel which is resistant to oxidation vunder heat containing about 6% to 10% chromium, 11/2% to 4.5% aluminum, and silicon within the usual ranges encountered in steel making practice, the remainder being principally iron.

-3. A: ferrous alloy comprising chromium between about 1% and 20%, aluminum between about .4% and 4.5% and silicon under 2% and not in excess of the aluminum, the balance being principally iron, and the sum ofthe silicon .and aluminum ranging between about .5% and 5.5% and the sum of the chromium, silicon'and aluminum amounting to at least 3.5%.

4. An alloy as specified in claim 3 in which the chromium is between 4% and 20% and the sum of the silicon and aluminum does not exceed 5%. y

5. An alloy Aas specified in claim 3 in which the chromium is between 4% and 17% and the sum of the aluminum and silicon is between about .7 5% and 5%.

6. An alloy as specified in claim 3 in which the chromium is between 5% and 16% and the sum of aluminum and silicon is between about .75% and 5%.

7. A ferrous alloy comprising chromium between about 1% and 10%, aluminum between about 1% and 4.5%, and silicon under 2% but not in excess of the aluminum, the

characterized by its resistance to hot oxidation, of substantially the following analysis: chromium between about 1% and 20%, aluminum between about .4% and 4.5%, and .silicon under 2% and not in excess of the aluminum, the balance being principally iron, and the sum of the silicon and aluminum ranging between about .5 and 5.5% and the sum of the chromium, silicon and aluminum amounting to at least 3.5%.

11. An alloy steel valve element for internal combustion engines characterized by its resistance to hot oxidation and by its forgeability and ability to be hardened, of an analysis within the following ranges: chromium between 4% and 18%, aluminum between about .4% and 4.5% and silicon under 2% and not in excess of the aluminum, the balance being principally iron, and in which the sum of the silicon and aluminum is between about 1% vand 4% for chromium in the middle range, but is not less than 1.5% for the lower end of the chromium range, or over 2.5% for the upper end of the chromium range.

12. An alloy steel valve for internal combustion engines characterized by its resistance to hot oxidation, 'of substantially the following analysis: chromium between about 1% and 10%, aluminum between about 1% and 4.5%, and silicon under 2%, but not in excess of the aluminum, the balance being principally iron.

13. An alloy steel valve for internal combustion engines, characterized by its resistance to hot oxidation, of the alloy specified in 100 claim 7.

14. An alloy steel valve characterized by its resistance to hot oxidation of substantially the following analysis: chromium about 9%, aluminum about 3%, and silicon within theV 105 usual ranges encountered in steel making practice but under 2 the balance being principally iron.

In testimony whereof, I have signed my name hereto.

PERCY A. E. ARMSTRONG.

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